Overuse injuries are common to those regularly performing activity as well as those with job related injuries. The site of failure in chronic overuse injuries are often musculotendinous structures. The most abundant component of musculotendinous tissue is collagen. Despite its ubiquity, collagen tissue is not well understood and is perceived to be rather inert. However, evidence is accumulating that collagen is quite dynamic. The purpose of this proposal is to further elucidate the processes of muscle and tendon collagen synthesis and degradation in response to mechanical loading and its deficiencies in overuse injuries. Specifically it is hypothesized that, 1) muscle and tendon collagen increase synthesis in response to exercise but these rates do not follow the same time course, 2) rates of muscle and tendon collagen degradation increase in response to exercise, 3) in subjects with an overuse tendon injury, rates of collagen synthesis in tendon (but not muscle) are transiently decreased compared to healthy tendon after an acute bout of exercise. To this end muscle collagen synthesis and degradation and its regulation will be studied with a combination of stable isotope tracers, tissue sampling, microdialysis, and molecular biology techniques during recovery from a strenuous bout of exercise in healthy subjects and those with patellar tendonitis. With elucidation of the patterns of collagen synthesis and degradation and where deficiencies lie in those with injuries, it will then be possible to design specific interventions to aid in restructuring.